OLE DB Constraints (SQL Server Compact)

Microsoft SQL Server Compact 3.5 (SQL Server Compact 3.5) supports constraints to enforce the data integrity rules in a database.

Constraints are added to columns using the ITableDefinitionWithConstraints interface. For foreign key constraints, the matchType element of the DBCONSTRAINTDESC structure should always be set to DBMATCHTYPE_FULL.

The SQL Server Compact 3.5 database engine does put some limitations on constraint types and how they function. For more information, see Understanding Databases (SQL Server Compact).

The following example shows how to use OLE DB to add a new UNIQUE constraint to the Extension column in the Employees table by using the ITableDefinitionWithConstraints::AddConstraint method.

// Declarations
HRESULT                         hr;
DBID                            TableName;  // name of table for new constraint
DBID                            ColumnList[1]; // name of column for new constraint
DBID                            ConstraintName; // name of new constraint
DBPROP                          dbprop[1];
DBPROPSET                       dbpropset[1];
DBCONSTRAINTDESC                rgConstraintDescs[1]; // Structure for constraint properties
IDBInitialize                   *pIDBInitialize       = NULL;        
IDBProperties                   *pIDBProperties       = NULL;        
IDBCreateSession                *pIDBCreateSession    = NULL;
ITableDefinitionWithConstraints *pITbleDefWithConstrt = NULL; // supports adding constraints

if (FAILED(hr = CoInitialize(NULL)))


// Create an instance of the OLE DB Provider
    IID_IDBInitialize, (void**)&pIDBInitialize);
    goto Exit;

// Initialize a property with name of database
// Open an exsiting database myDatabase
dbprop[0].dwPropertyID     = DBPROP_INIT_DATASOURCE;
dbprop[0].dwOptions         = DBPROPOPTIONS_REQUIRED;
dbprop[0].vValue.vt         = VT_BSTR;
dbprop[0].vValue.bstrVal = L"\\windows\\MyDB.sdf";

// Initialize the property set
dbpropset[0].guidPropertySet = DBPROPSET_DBINIT;
dbpropset[0].rgProperties     = dbprop;
dbpropset[0].cProperties     = sizeof(dbprop)/sizeof(dbprop[0]);

//Set initialization properties.
hr = pIDBInitialize->QueryInterface(IID_IDBProperties, 
(void **)&pIDBProperties);
    goto Exit;

// Sets properties in the Data Source and initialization property groups
hr = pIDBProperties->SetProperties(1, dbpropset); 
    goto Exit;

// Initializes a data source object 
hr = pIDBInitialize->Initialize();
    goto Exit;

// Get IDBCreateSession interface
hr = pIDBInitialize->QueryInterface(IID_IDBCreateSession,
if (FAILED(hr))
    //Send error-specific message and do error handling
    goto Exit;

// Create a session object. 
hr = pIDBCreateSession->CreateSession(NULL, IID_ITableDefinitionWithConstraints, 
    (IUnknown**) &pITbleDefWithConstrt);

// (This sample assumes that we have information about the Employees table
// database schema.)
// Prepare the table name DBID as Employees.
TableName.eKind          = DBKIND_NAME;
TableName.uName.pwszName = L"Employees";

// Prepare the list of columns that will receive the UNIQUE constraint. 
// In this case, just the Extension column. 
ColumnList[0].eKind = DBKIND_NAME;
ColumnList[0].uName.pwszName = L"Extension";

// Build the DBCONSTRAINTDESC structure needed to make the 
// ITableDefinitionWithConstraints::AddConstraint 
// call to add the constraint. 
rgConstraintDescs[0].pConstraintID = &ConstraintName;
rgConstraintDescs[0].ConstraintType = DBCONSTRAINTTYPE_UNIQUE;
rgConstraintDescs[0].cColumns = 1;
rgConstraintDescs[0].rgColumnList = ColumnList;
rgConstraintDescs[0].Deferrability = 0;  // Constraints are not deferrable.
// The following properties are not used in UNIQUE constraints
rgConstraintDescs[0].pReferencedTableID = NULL;
rgConstraintDescs[0].cForeignKeyColumns = 0;
rgConstraintDescs[0].rgForeignKeyColumnList = NULL;
rgConstraintDescs[0].pwszConstraintText = NULL;
rgConstraintDescs[0].UpdateRule = DBUPDELRULE_NOACTION;
rgConstraintDescs[0].DeleteRule = DBUPDELRULE_NOACTION;
rgConstraintDescs[0].MatchType = DBMATCHTYPE_NONE;

// Add the new constraint
hr = pITbleDefWithConstrt->AddConstraint(&TableName, rgConstraintDescs);


// When finished, clear the properties arrays and release interfaces.
// Uninitialize the environment.